1. Field of the Invention
The present invention relates to a photovoltaic device and a method of manufacturing thereof. More particularly, the present invention relates to a photovoltaic device such as a solar cell and a method of manufacturing thereof, by which light energy is converted directly to electric energy.
2. Description of the Prior Art
In the prior art, U.S. Pat. No. 4,281,208 is known as a photovoltaic device in which semiconductor photoactive film layers divided into a plurality of regions on the insulated surface of a substrate are respectively interposed between first and second electrode films to form a plurality of photoelectric conversion elements, which are electrically connected.
On the other hand, the applicant of the present invention filed Japanese Patent Application No. 213168/1982 (Japanese Patent Laying-Open Gazette No. 103383/1984) and U.S. Patent Application Ser. No. 617,724 filed June 6, 1984 concerning a manufacturing method most suitable for a photovoltaic device having the above described structure.
FIGS. 1 to 3 are cross-sectional views showing steps of a method of manufacturing of a conventional photovoltaic device and FIGS. 4 and 5 are enlarged sectional views showing an essential portion of a conventional photovoltaic device.
First, referring to FIGS. 1 to 5, a method of manufacturing of a conventional photovoltaic device will be described. As shown in FIG. 1, first, a semiconductor photoactive film layer 3 is provided over the whole area including the surfaces of the first electrode films 2a, 2b and 2c and the insulated surface of a substrate 1, the first electrode films 2a, 2b and 2c being disposed at predetermined distances. Then, a second electrode film 4 is formed over the whole surface of the semiconductor photoactive layer 3 without dividing the semiconductor photoactive layer 3 into the regions A, B and C.
Subsequently, as shown in FIG. 2, the second electrode film portions 4' and the semiconductor photoactive layer portions 3' located in the spacing regions ab and bc of the respective adjacent regions A, B and C are removed by etching so that second electrode films 4a, 4b and 4c and semiconductor photoactive layers 3a, 3b and 3c are individually separated.
Then, as shown in FIG. 3, connection electrode films 6a and 6b are selectively evaporated by using a mask so that the first electrode films 2b and 2c of the regions B and C are exposed on one side in the spacing regions ab and bc and these exposed portions 2ba and 2cb are electrically connected respectively to the second electrode films 4a and 4b of the adjacent regions A and B.
By the above described manufacturing method, photoelectric conversion elements A B and C comprising a laminated structure of first electrode films 2a, 2b and 2c, semiconductor photoactive layers 3a, 3b and 3c and second electrode films 4a, 4b and 4c, respectively are formed. The connection electrode films 6a and 6b for electrically connecting in series the photoelectric conversion elements A, B and C in the spacing regions ab and bc are sometimes incompletely evaporated which, to causes a rupture in an intermediate slanted portion because if the spacing region ab is taken for example as shown in FIG. 4, the connection electrode film 6a needs to cover a sharp height difference H arising as the sum of the thickness t.sub.1 of the semiconductor photoactive layer 3a and the thickness t.sub.2 of the second electrode film 4a. Such ruptures would occur more frequently if the connection electrode films 6a and 6b are made of a hard material.
Further, in the above described manufacturing method, as shown in FIG. 5 in an enlarged manner by taking the spacing region ab as an example, the faces 31a and 31b of the semiconductor photoactive layer portion 3' are excessively overetched. More specifically, prior to the masked evaporation of the connection electrode films 6a and 6b, an etching process is applied to the semiconductor photoactive layer portions 3' located in the spacing regions ab and bc. In this process, the faces 31a and 31b of the semiconductor photoactive layer portions 3' are overetched to a larger extent than the faces 41a' and 41b' of the etched second electrode film portions 4'. As a result, the contact faces of the second electrode films 4a and 4b facing the semiconductor photoactive layers 3a and 3b are undercut.
A photoresist film 5 is coated on the second electrode films 4a and 4b, so that the etchant can be prevented from penetrating into the portions of the second electrode films 4a and 4b not intended to be subjected to the etching process. The photoresist film 5 is removed immediately after the completion of the etching process. However, it was observed that at the time of removing the photoresist film 5, the edge portions 41a and 41b of the second electrode films 4a and 4b are curled upward due to the internal stress of the second electrode films 4a and 4b. Such undercutting due to overetching occurs to a greater or lesser extent both in a wet etching process using an etching liquid and in a dry etching process such as plasma etching by glow discharge in an atmosphere of etching gas. If such undercutting occurs due to overetching, a rupture might be caused in the intermediate slanted portions and the like of the connection electrode films 6a and 6b in the same manner as described above in connection with FIG. 4.
Further, if the edge portions 41a and 41b of the second electrode films 4a and 4b are curled, the connection electrode films 6a and 6b cannot be brought into contact with the slanted concave faces 31a and 31b of the semiconductor photoactive layers 3a and 3b respectively, even if the connection electrode films 6a and 6b extend over the curled edge portions 41a and 41b toward the exposed portions 2ba and 2cb of the first electrode films 2b and 2c in the spacing regions ab and bc, respectively, without being ruptured. As a result, a gap is formed between the connection electrode films 6a and 6b and the faces 31a and 31b and consequently, the slanted portions of the connection electrode films 6a and 6b are in a floating state and these slanted portions as well as the curled edge portions 41a and 41b cause the mechanical strength to be decreased. Accordingly, instance of rupture in the case where the edge portions 41a and 41b of the second electrode films 4a and 4b are curled occur with an extremely high frequency as compared with the case in FIG. 4.